In the field of analytical chemistry, there is a need for improved liquid dispensing devices to probe samples of interest. In particular, in biochemistry a technique called Western Blot analysis requires the timed application of at least three aqueous solutions to probe a membrane which contains samples of interest. The samples are usually proteins, but can also be DNA or carbohydrates. The samples are usually separated into individual molecular species by SDS-PAGE electrophoresis followed by electroblotting on to the membrane. Direct application of pure or complex samples has also been used by pipetting onto the membrane. The membrane binds the sample molecules due to its hydrophobic nature (PVDF membranes) or covalent crosslinking (nitrocellulose membranes). The membrane can then be probed with various detection procedures which identify the particular chemical of interest. It is this last step that requires sequential application of two to five solutions in a timed schedule.
There are presently four methods of probing the membranes described above: 1) manual application of solutions with several timed incubations over a period of about four hours; 2) automated machines that apply a similar routine as the manual operator; 3) a filter paper capillary device that applies one routine (e.g., iBind device by Life Technologies); and 4) a vacuum based method that moves solutions across a membrane by suction (e.g., SNAP id device by EMD Millipore Inc.). All four approaches aim to achieve a similar routine: first, block the membrane with a non-specific solution of protein, DNA, or carbohydrate, which will reduce background noise in the final result; second, in some scenarios a wash step is included; third, the specific analytical reagent (SAR) or primary reagent is added, which binds to the desired target molecule to be measured; fourth, one to six wash steps to remove excess SAR; fifth, application of a second generic reagent that amplifies the signal of the first; and finally, application of 1 to 6 washes with buffer to remove excess reagent. The membrane is then ready for signal development in colorimetric, fluorescence, radiometric, or luminescence modes.
This six step procedure is very time consuming and labor intensive. The operator has to return to the membrane once per hour in the reagent incubation steps and every 3 to 5 minutes in the wash steps, for a total of between 10 and 17 times. In addition, different operators prefer to run different procedures. For example, a first operator may desire to use 3×5 washes and a 2 hour SAR step and a 1 hour secondary reagent step, whereas a second operator might use a 16 hour SAR and only one wash step.
The machines that have been developed to date allow a user to control wash times and reagent incubation times and address the need for automation. However, the machines are highly complex with various combinations of pumps, pressurized air supply and/or actuators, and require a trained individual to operate them. For example U.S. Pat. Nos. 4,859,419, 8,404,198, 5,567,595, 5,559,032, 6,194,160, 4,585,623, and 8,758,687, as well as iBind machine (internet at: tools.lifetechnologies.com/content/sfs/manuals/ibind_man.pdf) and the Snap id machine (internet at: emdmillipore.com/US/en/life-science-research/protein-detection-quantification/SNAP-i.d.-2.0-Protein-Detection-System-/snap-id-system-western-blotting/m9Wb.qB.wzoAAAFBrt8RRkwt.nav) report various machines, some of which are complicated and/or inflexible and require trained personnel to operate and maintain, which makes operation and repair expensive. Thus, there is a need to reduce complexity and costs of manufacture.
The present disclosure addresses many of the drawbacks of the presently available devices.